1. Technical Field
The present invention relates generally cellular wireless communication systems; and more particularly to a wireless communication system having an architecture that is scalable to compensate for loading levels, able to service any subscriber distribution and compliant with existing standards of operation and in which signaling messages specially routed to servicing system components based upon the content of the signaling messages.
2. Related Art
Wireless communication systems are generally known in the art to service wireless communications within a service area. The construction of a wireless communication system typically includes a plurality of base stations dispersed throughout the service area. The base stations couple to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC-couples to a mobile switching center (MSC) that also couples to the public switched telephone network (PSTN) and to other MSCs. Mobile units operating within the wireless communication system establish communication with one or more of the base stations. The structure of the wireless communication system is hierarchical such that the load served by the base stations is routed via a predetermined path through a designated BSC to a designated MSC.
When the resources of the wireless communication system are insufficient to service load in a particular area, not all call requests will be serviced. Such insufficient capacity causes calls to be dropped, calls to be blocked and produces an overall degradation in system performance. Failing to service customers results in the loss of customers as well as a reduction in the revenue that would otherwise be generated by servicing the calls. Thus, it is extremely important to service as many calls as possible so that subscribers remain with the service provider and so that revenues are maximized.
System capacity may be limited by various components within the system. For example, base stations may become overloaded and fail to service subscribers requesting service. In such cases, as load grows within a particular portion of the system, additional base stations are deployed to handle the additional traffic. Likewise, when a number of base stations connected to any BSC provides overloads the BSC, additional BSCs are deployed to service the increased load.
MSCs also may become overloaded. The central processing unit and switching capacity of an MSC may only support a maximum level of traffic, messaging and overhead processing. As the capacity of existing MSCs is exhausted, additional MSCs must be introduced into the network. Of course, in the initial deployment of a system, an overall goal is to support the highest number of subscribers with the smallest infrastructure, typically including only a single MSC. This initial deployment not only minimizes the initial cost of deployment but reduces the networking overhead that results from subscriber mobility.
When an MSC (or multiple MSCs) serving a system become overloaded, additional MSCs must be deployed. In deploying additional MSCs within a system, the area served by the system is typically geographically partitioned to equalize loading among the MSCs. As the number of deployed MSCs increases, each served area becomes smaller and the number of boundaries between serving MSCs increases. The additional boundaries cause an increase in subscriber mobility between MSCs, the subscriber mobility consuming additional MSC CPU capacity. Resultantly, as additional MSCs are added within a system, the marginal benefit of each MSC deployment is reduced as the total number of deployed MSCs increases.
Further disadvantages of deploying MSCs relate to the partitioning of the service area. In determining where partitions between MSCs should be placed, an expensive and time consuming study is performed in an effort to equalize loading among MSCs in a manner which minimizes mobility overhead. Then, based upon the study, the system infrastructure must be physically altered and reprogrammed according to the partition. Such operations cause the system to be inoperable for periods of time during which subscribers are not served. Further, due to the difficulty in implementing the partition, system operators generally do not exactly implement the proposed partition which results in unbalanced load and reduced capacity.
Thus, there is a need in the art for a system and associated method of operation which allows additional MSCs to be deployed within a wireless communication system so that system capacity is increased accordingly and so that added overhead in system operation is minimized.
In order to overcome the described shortcomings of prior wireless communication systems, among other shortcomings, a wireless communication system constructed according to the present invention assigns each mobile unit to a serving mobile switching center among a plurality of mobile switching centers to equalize loading on the mobile switching centers. The wireless communication system includes the plurality of mobile switching centers and a base station system which includes a plurality of base station controllers, each of which couples to a plurality of base stations. To minimize mobility overhead, each mobile unit is served only by its serving mobile switching center. Signaling messages required to service a particular mobile unit are routed to its serving mobile switching center by utilizing the mobile unit""s temporary identification number. Since no inter-mobile switching center hand-off and location updating are required, mobility overhead is significantly reduced. Also, assignment of mobile units to mobile switching centers can be performed in such a manner to equalize loading among the plurality of base stations.
In one particular construction of the wireless communication system, a message router couples the base station system to the plurality of mobile switching centers for purposes of signaling message routing and, in some cases, for the purpose of assigning mobile units to mobile switching centers. In an example of operation, upon attachment of a mobile unit to the system, the message router determines the loading on each of the mobile switching centers. Based upon the loading, the message router assigns the mobile unit to one of the mobile switching centers, the xe2x80x9cservingxe2x80x9d mobile switching center. The serving mobile switching center then assigns a temporary identification number (temporary ID) to the mobile unit that identifies itself as the serving mobile switching center. The temporary ID also uniquely identifies the mobile unit. The mobile unit stores the temporary ID in its local memory and uses the temporary ID to identify itself in future signaling connections.
During a subsequent operation, in which a signaling message is sent by a base station controller on behalf of the mobile unit (the signaling message containing the temporary ID), the message router intercepts the signaling message. The message router then extracts the temporary ID, determines the serving mobile switching center from the temporary ID, and routes the signaling message to the serving mobile switching center. The serving mobile switching center then may service the mobile unit, based upon the signaling message contents. Once the serving mobile switching center is determined, operation is transparent to the serving base station controller and the serving mobile switching center. Further, because of the nature of its operation, the loading on the message router is small.
In another particular construction, each of the base station controllers couple to each of the mobile switching centers via a network. In such case, each of the base station controllers and each of the mobile switching centers includes additional equipment which performs at least a portion of the operations of the message router. The network may be dissimilar to a conventional data structure supported by the wireless communication system. For example, the network may be packet switched network. In such case, data conversions must be performed for the base station controllers and mobile switching centers to operate in conjunction with the network. With such operations supported, a conventional data network may be employed to service the traffic between the base station controllers and the mobile switching centers.
In the operation of such a network-based construction, with the message router function incorporated into the base station controllers, the base station controllers initially assign mobile units to the mobile switching centers to balance load. In such assignment operations, the mobile switching centers assign temporary IDs from their own pool of such numbers. Each number in the pool identifies the mobile switching center. Alternatively, a message router may be connected to the network, with the message router performing the load balancing operations and assigning mobile units to their serving mobile switching centers. In either case, when traffic is serviced, the traffic passes across the network between a serving mobile switching center and a serving base station controller.
By equalizing load among the plurality of mobile switching centers, operation according to the present invention increases system capacity. With each of the mobile switching centers serving the whole service area, subscriber mobility overhead is substantially reduced. Thus, the deployment of an additional mobile switching center provides substantial benefit. Further, because the system need not be partitioned, substantial effort is eliminated.
Moreover, other aspects of the present invention will become apparent with further reference to the drawings and specification which follow.